The cutting chambers of riding lawn mowers can discharge large amounts of grass clippings at high rates, particularly as mower sizes and speeds increase. Typically, a cutting chamber has a rotating cutting blade which cuts grass primarily at its tips, and also functions like a fan or blower by powering a vortex of rotating air inside the cutting chamber. This cutting chamber vortex lifts and transports grass clippings around the periphery of the cutting chamber above the cutting blade until the grass clippings are blown out through a discharge opening in the side of the cutting chamber. Of concern here is the discharge of grass clippings from a cutting chamber. A side discharge mower can evenly broadcasts clippings across the turf as the mower moves forward because, if the clippings are broadcast in a direction that is generally perpendicular to the direction in which the mower is moving. In some other side discharge configurations, however, it is desirable to further control or fan the clippings over a particular area or into a particular distribution. With a rear discharge mower, grass clippings may tend be dispersed unevenly or possibly distributed in windrows behind the mower. These results occur because the direction in which grass clippings are discharged is generally parallel to the path of the mower.
In the case of a rear discharge cutting deck, the outboard side of a discharge opening is usually defined by a straight, tangentially extending portion of the sidewall of the cutting chamber. The rotating grass clippings follow the straight portion of the sidewall and exit the cutting chamber through the discharge opening. It is usually preferable to spread grass clippings as evenly as possible. But, the distribution of grass clippings depends on the type of grass, the length of the clippings and the moisture content or density of the clippings. If the discharge opening has a fixed geometry, then, in some situations, the clippings will accumulate in windrows, or the clippings will be deposited in clumps. What is needed is a discharge opening that can be adjusted to compensate for different types of grass clippings, different types of mowing conditions, and different types of mowing deck geometries so that grass clippings can be manipulated, in order to focus the grass clippings or distribute them as evenly as possible.